1. Field of the Invention
The present invention generally relates to methods for flow control, and more particularly to a flow control method directed to a hand-over process inherent in a telecommunication system in which an ATM system is applied to a multimedia mobile telecommunication network of a microcell system.
2. Description of the Related Art
Recently, there has been considerable activity in the research and development of a high-rate multimedia transmission in mobile telecommunications. Such a system is required to reduce the transmission power. It is thus required to reduce the telecommunication zone (cell) covered by a single base station and to employ a radio zone as narrow as approximately 100 m. It should be noted that the zone covered by one base station in a conventional automobile or portable telephone system is as large as approximately a few kilometers. When the radio zone is narrow as described above, a mobile station traveling at a high speed will go out of the current radio zone soon and enter another radio zone. Hence, it is required to use a hand-over process directed to prevent a communication from being interrupted. The hand-over process switches the base stations when the mobile station travels over radio zones so that the mobile station can continue to communicate with the other station.
In the conventional mobile telecommunication system, a communication is instantaneously broken for a time of 0.7-0.8 seconds when the channel used in the communication is switched. This is caused by an event in which data transferred over a transmission path is merely lost during the hand-over process. The instantaneous break of communication causes a loss of speech or data and results in a degradation in the communication quality. Particularly, the instantaneous break is a serious problem when data is transferred between data processing devices such as computers. Generally, if a loss of data occurs, a retransmission of data is required. However, such a data retransmission increases traffic. If a relatively narrow radio zone is employed, the hand-over should be frequently carried out. In this case, it is very important to consider problems due to the instantaneous break. In order to eliminate the problems caused by the instantaneous break, it is necessary to improve not only the radio channel switching technique but also the flow control of the whole telecommunication system and to thus prevent data from being lost during the hand-over process.